package com.xmg.dataStructure.tensuanfa;

import java.util.Arrays;

/**
 * 使用弗洛伊德算法计算邻接矩阵最短路径问题
 *
 * @Author: mazhongqing
 * @Date: 2021/3/16 15:15
 */
public class FloydAlgorithm {
    public static void main(String[] args) {
        // 测试看看图是否创建成功
        char[] vertex = {'A', 'B', 'C', 'D', 'E', 'F', 'G'};
        //创建邻接矩阵
        int[][] matrix = new int[vertex.length][vertex.length];
        final int N = 65535;
        matrix[0] = new int[]{0, 5, 7, N, N, N, 2};
        matrix[1] = new int[]{5, 0, N, 9, N, N, 3};
        matrix[2] = new int[]{7, N, 0, N, 8, N, N};
        matrix[3] = new int[]{N, 9, N, 0, N, 4, N};
        matrix[4] = new int[]{N, N, 8, N, 0, 5, 4};
        matrix[5] = new int[]{N, N, N, 4, 5, 0, 6};
        matrix[6] = new int[]{2, 3, N, N, 4, 6, 0};

        Graph graph = new Graph(vertex.length,matrix,vertex);
        graph.floyd();
        graph.show();
    }
}

class Graph {
    private char[] vertex;    //存放顶点的数组
    private int[][] dis;        //从各个顶点出发到其他顶点的距离，最后的结果也保留在该数组
    private int[][] pre;        //保存到达目标顶点的前驱顶点

    public Graph(int length, int[][] matrix, char[] vertex) {
        this.vertex = vertex;
        this.dis = matrix;
        this.pre = new int[length][length];
        for (int i = 0; i < length; i++) {
            Arrays.fill(pre[i], i);
        }
    }

    //显示pre数组和dis数组
    public void show() {
        char[] vertex = {'A', 'B', 'C', 'D', 'E', 'F', 'G'};
        for (int k = 0; k < dis.length; k++) {
            //先将pre数组输出每一行
            for (int i = 0; i < dis.length; i++) {
                System.out.print(vertex[pre[k][i]] + " ");
            }
            System.out.println();
            //输出dis数组的一行数据
            for (int i = 0; i < dis.length; i++) {
                System.out.print("(" + vertex[k] + "到" + vertex[i] + "的最短路径是" + dis[k][i] + ") ");
            }
            System.out.println();
            System.out.println();
        }
    }

    public void floyd(){
        int len = 0;//变量保存距离
        //对中间顶点遍历，k就是中间顶点的下标
        for (int k = 0; k < dis.length; k++) {

            for (int j = 0; j < dis.length; j++) {

                for (int i = 0; i < dis.length; i++) {
                    len = dis[i][k] + dis[k][j];
                    if(len<dis[i][j]){
                        dis[i][j] = len;//更近的距离
                        pre[i][j] = pre[k][j];
                    }
                }
            }
        }
    }
}
